Wire plating apparatus including doctoring die

ABSTRACT

The invention relates to a device for tin plating copper jump wires. The copper wire passes through a tin bath and is guided through a stripper nozzle, whose outlet opening is below the plane of the bath surface. The bore of the stripper nozzle possesses a wave shaped cross section. For a wire diameter of 0.5 mm, 4 to 20 half waves are provided and the diameter of the bore and the depth of the half waves are adjusted to the diameter of the wire. The tin plated copper wires have a uniform tin layer with a thickness &gt; 3 Mu m and are extremely well solderable.

United States Patent Schreiner et a1.

[ Dec. 25, 1973 WIRE PLATING APPARATUS INCLUDING DOCTORING DIE Inventors: Horst Schreiner; Henryk F idos, both of Nurnberg, Germany Siemens Aktiengesellschaft, Berlin, Germany Filed: Jan. 29, 1973 Appl. No.: 327,852

Related US. Application Data Continuation-impart of Ser. No. 88,285, Nov. 10,

1970, abandoned.

Assignee:

Foreign Application Priority Data Nov, 13, 1969 Germany P 19 57 033.4

US. Cl. 118/125 Int. Cl. B05c ll/02 Field of Search 118/125, DIG. 19, 118/DIG. 20, DIG. 18, 404, 405, 420;

References Cited UNITED STATES PATENTS 3/1935 Adams 118/125 X 2,036,048 3/1936 Hinsky ll8/DIG. 18 2,080,518 5/1937 Underwood ll8/DlG. 18 2,429,870 10/1947 Dahlstrom 118/125 3,203,826 8/1965 Stobierski 118/125 X 3,402,696 9/1968 Richards 118/125 FOREIGN PATENTS OR APPLICATIONS 313,572 12/1933 Italy 118/125 471,376 5/1952 Italy 118/125 Primary Examiner-Morris Kaplan Attorneyl-lerbert L. Lerner et al.

[57] ABSTRACT The invention relates to a device for tin plating copper jump wires. The copper wire passes through a tin bath and is guided through a stripper nozzle, whose outlet opening is below the plane of the bath surface.

The bore of the stripper nozzle possesses a wave shaped cross section. For a wire diameter of 0.5 mm, 4 to 20 half waves are provided and the diameter of the bore and the depth of the half waves are adjusted to the diameter of the wire.

The tin plated copper wires have a uniform tin layer with a thickness 3 pm and are extremely well solderable.

6 Claims, 5 Drawing Figures PATENTEDDEB25I9T3 3.780.698

SHEET 2 [IF 2 WIRE PLATING APPARATUS INCLUDING DOCTORING DIE The present invention is a continuation-in-part of Application Ser. No. 88,285, filed Nov. 10, 1970 and now abandoned.

Our invention relates to a method of producing tin layers or tin alloy layers on copper or copper alloy wires having a diameter of 0.5 mm. The method is effected by hot tin plating at a uniform thickness of 3 p. across the wire circumference. The wire is then passed through a tin bath or a tin alloy bath and is guided through a profiled stripper nozzle.

For an impeccable solderability of thick tin plated copper jump wires, a minimum layer thickness of 3 p. tin or tin alloys is required for each place of the wire. Various tin plating methods for producing copper jump wires have been suggested or made known, whose aim is to provide the copper wires with adhering, uniformly thick, good solderable tin layers. To this end, the copper wire may be appropriately treated, prior to its insertion into the tin bath, as well as following its emergence from the tin bath.

It is known, for example from German Disclosure Document 1,521,487, to produce a tin layer of medium thickness, between 3 and 10 u, on wires of copper or copper alloys. This is done by hot tin plating a tin layer placed upon a circular cross section wire during its passage through a stripper nozzle with polygonal cross section and to distribute the tin to a medium layer thickness that fluctuates across the circumference of the wire but is uniform in the sectors. It is then formed immediately thereafter into a uniform layer thickness, with a calibrating nozzle of uniform cross section.

British Patent 921,755 makes known, for example, to arrange a stripper nozzle on the surface of the tin bath. This stripper nozzle possesses a bore with circular cross section. Since, in the device described in the British Patent 921,755, the wire leaves the tin bath at the bottom of the bath container, the stripper nozzle is to prevent, in the first place, the running out of the tin bath.

The known method is affiliated with short-comings with respect to continuous manufacture. Above all, fluctuations in layer thickness occur and it is difficult to adjust the layer thickness. It is an object of the invention to overcome these disadvantages.

The present invention has as its object overcoming the above disadvantages.

For a method of the afore-described type, the invention accomplishes this object by using a stripper nozzle whose outlet opening is situated below the bath surface.

The outlet opening may be arranged at least 5 mm below the bath surface. It is preferable to select a distance in the bath between the inlet opening of the stripper nozzle and the last contact point, which space will suffice for the formation of a laminar flow in the vicinity of the moving wire. At a wire velocity of l to 3 m/sec. a distance of at least cm may be adjusted between the inlet opening and the last point of contact.

It is preferable to use a stripper nozzle, whose bore diameter is bordered by a wave train. The wave train runs between two concentric circles. The radii of the circles are adjusted to the radius of the wire and 3 to half waves are provided for each millimeter of the circumference of the inner, concentric circles. A stripper nozzle with 5 to 8 half waves per millimeter of the circumference, may be used.

The temperature of the stripper nozzle may be determined by the bath temperature.

The apparatus of the invention provides tin plated copper jump wires with a tin layer of uniform thickness, across the entire circumference of the wire. The immersion of the stripper nozzle into the tin bath produces a hydrostatic pressure in the lower portion of the nozzle which increases as the immersion depth becomes greater.

The copper jump wire, which enters the tin bath, results in a laminar flow in the tin bath. In the method of the invention, the parameters are so adjusted that this laminar flow is not disturbed up to the inlet of the copper wire into the stripper nozzle. The uniform tin layer is obtained through the built-up hydrostatic pressure, the laminar flow in the vicinity of the moving wire and the geometry of the profiled stripper nozzle. The geometry of the profiled stripper nozzle prevents the Bernoulli effect, the so-called hydrodynamic pressure, which results in assymetrical positions of the wire within the stripper nozzle when nozzles of circular cross section are employed. The resulting formation of sicle-shaped tin layers on the copper wire is avoided thereby. The selection of the wave level, that is the selection of the distance between the two concentric circles between which the wave train proceeds the immersion depth of the nozzle below the bath level and the wire velocity, determine the layer thickness. During the adjustment to the wire radius, the tolerance limits for the wire radius may be taken into consideration. This adjustment of the tin layer thickness may also be effected for high wire velocities, that is for wire velocities above 1 m/sec. Thus the method of the invention may be applied many-fold and extremely economical. The immersion of the profiled stripper nozzle into the'tin bath, moreover, eliminates possible introduction of tin oxides into the tin layer of the wire. The tin which is situated beneath the inlet opening of the stripper nozzle is being continually renewed by the moving tin boundary layer which is carried along by the tin wire, as only one portion of this boundary layer enters the nozzle. The tin bath region immediately ahead of the inlet opening is therefore very clean and pure and free of oxide. Thererefore, it is also not necessary to use organic substances, for example oil, as a cover on the tin bath, as is customary in the known methods. Hence, no cracking products, which frequently lead to a disturbance of the tin layer, are developed. In order to keep the bath clean, the remaining tin bath surface may be covered by iron sheets. A part of the exposed tin bath surface, situated in the region where the wire enters into the tin bath, is covered with charcoal. This limits the free tin layer, which reacts with air to a minimum. Furthermore, when pure tin baths are used, the temperature can be lowered to 260C. As a result thereof, a lower dissolution of copper from the wire into the tin bath occurs, since the dissolving speed is lower due to the decrease in bath temperature. Also, due to the low bath temperature, the cooling path is considerably decreased up to solidification of the tin layer. In the known methods, tin fountains are carried along during high through passage speeds, together with the copper wire which emerges from the tin bath surface.

According to the solution of the invention, the wire velocity could be increased up to 10 m/sec. at which disturbances due to tin spraying did not occur. It is therefore possible to increase the output by the factor 2 to 3, per strand and in some cases even by the factor 10.

Finally, it is advantageous that the stripper nozzle does not have to be heated separately. The stripper nozzle is heated directly by the tin bath and the temperature of the stripper nozzle is in a state of equilibrium, usually close to the temperature of the tin bath.

The solderability of the copper wires tin plated, according to the invention, may be tested according to the solder ball test. Testing conditions for a wire diameter of 0.5 mm, are a solder ball weight of 75 mg when SnPb 40 is used as solder and a testing temperature of 235C. The clamped wire is dipped into a liquid solder pearl and the time which elapses until the solder drop encloses the entire wire is measured. In wires, which are tin plated according to the invention, the solder periods are considerably below a second, even if changes have taken place for many days, for example by tempering. Due to this good solderability, the copper wires tin plated according to the invention are also suitable for automatic soldering processes such as for example, sonic or immersion wleding.

A preferred device for performing the method of the invention is provided with a stripping nozzle, where the radius of the inner-one of the concentric circles, wherebetween the wave train proceeds, is l to 10 u, preferably 2.5 to p. larger than the upper tolerance limit for the radius of the wire. Preferably, a stripper nozzle is provided where thedifference between the radii of the inner and the outer one of the concentric circles, wherebetween the wave train proceeds, is 20 to 80 p, preferably 40 to 60 u.

The half waves of the wave train which contact the outer of the concentric circles may be shaped at least nearly as a circular arc. I

it is preferable to provide as an inlet opening of the stripper nozzle a tube which is situated concentrically to the bore of the stripper nozzle. The inside diameter of the tube may be up to 1.5 mm larger than the wire diameter. The tube may be up to 100 mm long.

The stripper nozzle may be comprised of diamond, ruby, a hard metal or stainless steel. The stripper nozzle may be arranged in a holder, which is so designed that the stripper nozzle may be moved parallel to the plane of the bath surface, in pulling direction and opposite to the pulling direction of the wire. The stripper nozzle may be inserted into a tube. According to a known manner, the wire may be deflected in the bath with a roller and be removed from the bath at least almost perpendicularly. The deflection rollers and the stripper nozzle may be rigidly interconnected, whereby the distance between the roller and the outlet opening of the stripper nozzle, is adjustable. The distance between the inlet opening of the stripper nozzle and the deflection roller is preferably at least cm. The location of the stripper nozzle in a holder ensures convenient servicing and handling during the rethreading of a wire within a roller. Moreover the connection of the stripper roller and the deflection roller into one unit makes the threading of the wire considerably easier.

FIG. 1 is a schematic illustration of a thick tin plating installation;

FIG. 2 is a stripper nozzle;

FIG. 3 is an enlarged section of the stripper nozzle of FIG. 2;

FIG. 4 schematically illustrates the tin bath in enlarged sections with a stripper nozzle below the surface; and

FIG. 5 shows a variation of FIG. 4.

The following is a disclosure of the method relating to the invention and a device for performing said method, with reference to FIGS. 1 to 5.

FIG. 1 schematically illustrates a thick tin plating installation. The copper jump wire l is removed from reel 2, in the direction shown by the arrows. After two deflection rollers, the wire passes first in an annealing furnace 3, through a water vapor atmosphere, at 800 to 900C, where its surface is purified. The required stretching values of 27 to 30 percent are further ad- !5 justed by annealing. Thereafter, the annealed wire 1 enters a bath 4. Following the water bath, the water is stripped off the wire surface with the aid of a drying brush 5. The copper wire passes through an etchant solution section (l-lCl acid) 6 to remove surface layers, and enters the tin bath 7. The HCl etchant section consists of a dropping vessel, filled with hydrochloric acid. The dropping vessel is situated above strippers which may be produced of felt. The felt strips are saturated with hydrochloric acid, with the aid of the dropping vessel.

In the tin bath 7, the wire 1 is deflected with a deflection roller 8 and leaves the tin bath 7 at least nearly vertical, the tin bath 7 is covered with charcoal 9, at least in the region of the inlet point of the wire 1, in order to prevent contamination of the tin bath 7, for example, an oxidation of the tin surface.

The copper jump wire 1, which emerges from the tin bath 7, is guided through a stripper nozzle 10, whose outlet opening is arranged below the tin bath surface. The stripper nozzle 10 is installed into a tube 11 and forced, with said tuber, under the surface of the tin bath 7. We have previously pointed out in detail the advantages of this device wherein an hydrostatic pressure is developed in the inlet opening of the stripper nozzle 10 and where contamination with oxidation products is eliminated in the region of the inlet point of the wire 1. After passing a cooling path 12, where the wire 1 is air cooled, the wire is deflected via rollers 13 and 14 and guided to a take up device, not shown in FIG. 1.

The stripper nozzle has a bore with a wave profile. The inner diameter of the bore and the depth of the waves are adjusted to the diameter of the copper wire. This adjustment will be seen from the subsequent Figures.

The stripper nozzle 10 is heated by the tin bath up to almost the temperature of the tin bath. The outlet opening of the stripper nozzle 10 should be at least 5 mm below the tin bath surface. Also, at a wire velocity between 1 and 3 m/sec. the distance between the inlet opening of the stripper nozzle 10 and the deflection roller 8 should be at least 10 cm. In the vicinity of the moving wire, a laminar flow begins to develop. This laminar flow is disturbed by the deflection roller 8 or by the presence of another solid body which contacts the moving wire in the tin bath. The distance between the inlet opening of the stripper nozzle 10 and the deflection roller 8 must be selected to be so high as to provide the formation of new undisturbed laminar flow in the region of the moving wire 1, during its entry into the stripper nozzle 10. A uniform layer thickness is insured during the tin plating of the wire through the profiling of the stripper nozzle, the hydrostatic pressure and through the laminar flow in the region of the wire entering the stripper nozzle 10.

FIG. 2 illustrates a section through a stripper nozzle 10, with a copper wire 1 is also shown in section in the bore 15 of the stripper nozzle. The bore 15 of the stripper nozzle 10 has a wave profile. In FIG. 2, two concentric circles 16 and 17 are shown with radii R, and R The wave train 18 runs between the concentric circles 16 and 17. The wave train 18 has between 3 and 15, and preferably five to eight half waves, per millimeter of the circumference of the inner circle 16. FIG. 2 shows a nozzle for a wire radius R of 0.25mm. A closed wave train with eight half waves is provided, this corresponds to at least five half waves relative to a unit length. The radii R and R and thus the depth (R, R of the half waves of the wave train 18 are adjusted to the radius R of the wire. Determining this adjustment are the tolerance limits for the wire radius R and the desired layer thickness for the tin plating. The tolerance limits for the wire diameter R enter essentially in the radius R, of the interior concentric circle 16. This radius must be selected at least large enough so as to prevent, during the passage of the wire 1, the wave profile from being embedded in the wire surface. It is preferred that R, is between 1 and 10, preferably 2.5 to 5 p. greater than the upper tolerance limit for the wire radius R The layer thickness is essentially determined by the depth R R, of the individual waves and by the distance between the wave maximum and minimum, that is the number of half waves per millimeter of the circumference.

'FIG. 3 illustrates an enlarged section of the stripper nozzle l0 according to FIGS. 2-3 and shows that the half waves 18a, which touch the outer concentric circle 17, are preferably shaped at least nearly as a semicircle. The radius r of a circle 19 drawn into a half wave 18a and the chord c which is defined by the intersecting points of the circle 19 with the inner concentric circle 16, are decisive for the layer thickness, next to the difference between the diameters R, and R of the concentric circles 16 and 17. The radius r or the length of the chord c is determined by the number of half waves of the wave train 18. It was found that for a layer thickness which ranges between 3 u and about 7 u, the number of half waves per millimeter of the circumference R, of the circle 16, must be between 3 and 15. The difference R R, between the radii R and R of the concentric circles 16 and 17 may vary between 20 and 80 [.L, preferably from 40 to 60 p. The tin layer adhering to the wire is profiled with a thus dimensioned stripper nozzle. The subsequent smoothening is effected by itself through the surface tension of the profiled tin layer, whereby the form of profiling provides a uniform, average layer thickness of at least almost constant size, over the entire wire circumference. This provides the aforedescribed advantages and the excellent solder characteristics of the copper jump wire tin plated in accordance with the method of the invention.

Stripper nozzle is made of diamond, ruby, hard metal or stainless steel, in order to obtain the best possible stability therefor.

The production process begins with a stripper nozzle with a circular bore whose diameter 2 is R,. To produce a stripper nozzle according to FIG. 2 with 8 half waves for a wire radius R of 0.25 mm, the nozzle is clamped into a octagonal holder and a tungsten wire with diameter r is threaded through the bore of the nozzle and moved back and forth in exact guidance. The polishing means may be a diamond board. The processing is carried out in steps and the wave depth is measured by microscope. After a half wave is ground out, the clamping device is placed upon the next polygonal surface so that one by one all half waves shaped in a circular are are worked in. The sharp edges are subsequently rounded off by after-polishing. For instance, when a 0.500 mm thick copper wire with tolerance limits between 0.497 to 0.508 mm is to be tin plated, the profiled nozzle 10 having 8 half waves is dimensioned as follows: radius R, 0.259 mm; radium R 0.299 mm. When thick tin plating was performed with this profiled stripper nozzle which was placed into a device according to FIG. 1, a pure tin bath of a temperature of 260C was used. A tube 11 of stainless steel was used for inserting the stripper nozzle 10. The outlet opening of the stripper nozzle 10 was mm below the level of the tin bath. The distance of the deflection roller from the profiled stripper nozzle was about 20 cm. The copper jump wire had a pay out velocity of l m/sec. A uniform tin layer thickness of 5 [.L was obtained over the entire wire circumference and the wire length. This average tin layer thickness was measured according to the electrochemical removal process. The uniformity of the tin layer thickness along the wire circumference was determined at cross ground sections of the tin plated wire, with the aid of light optics. Even when this wire was stored at lC in air for four days, an impeccable wetting of the solder ball was obtained with the afore-described solder ball test within a period considerably below one second. Thus this wire has very good solderability.

FIG. 4 shows the tin bath of FIG. 1, in enlarged illustration. The tin bath 7 is placed into a container 20 and may be heated. A heating device is not shown in FIG. 4 in order to preserve the clarity. Also, not found in FIG. 4 is the charcoal covering 9, which is shown in FIG. 1. The copper wire 1 enters the tin bath 7 and is deflected by deflection roller 8 and leaves the tin bath at least almost perpendicularly. The stripper nozzle 10 is so arranged that the outlet opening 14a of the bore 14 is situated at the distance b below the surface of the tin bath 7. The distance b should be at least 5 mm. The size of the distance b helps to adjust the hydrostatic pressure which is produced in inlet opening 14b through the immersion of the stripper nozzle 10 into the tin bath.

The distance between the deflection roller 8 and the inlet opening 14b is indicated as a in FIG. 4. This distance a should be sufficiently great, as previously indicated, that the laminar flow which had been'disturbed by the deflection roller, may again fully develop in the vininity of the moving wire, up to its entry into the inlet opening 14b. At a wire velocity between 1 and 3 m/sec. the distance a should amount to at least 10 cm.

The stripper nozzle 10 is in a tube 11 which, for example, may be of stainless steel. The tube 11 is held with a circular ring 21. The tube 11 is movable in the direction of its longitudinal axis within the circular ring 21. The movement of the tube 11 is limited by an upper flange 22 and a lower flange 23 which are attached at the tube 11. The circular ring 21 is positioned in a round box 24 which is affixed, via an arm 25, to structure 26, which supports the deflection roller 8. The distance a between the inlet opening 14b of the stripper nozzle 10 and the deflection roller 8, may be adjusted by arm 25. Moreover, this device has the advantage that the stripper nozzle can simultaneously be removed with the deflection roller 8, from the bath 7. This makes the threading of the wire 1 much simpler.

The holder for the tube 11 which consists of the circular ring 21 and the round box 24, insures a certain mobility of the stripper nozzle 10. The round box 24 has openings 27 and 28 at its bottom and at its top. The diameter of these openings is essentially smaller than the diameter of the circular ring 24 but larger than the diameter of tube 11.

The circular ring 21 is positioned in the interior of the round box bearing on the bottom and is therefore movable parallel to the plane of the bath surface, in all directions. The tube 11 is also movable, in the circular ring 21, in the direction of its longitudinal axis. While the device is in operation, the tube 11 will assume approximately the position shown in FIG. 4, as a result of the pressure which is being exerted at the inlet opening 14b, against the stripper nozzle 10. Hence, during operation, the tube 11 and thus also the stripper nozzle are movable during sudden disturbances in the pulling direction of the wire I, as well as to a slight degree, in opposite direction of the wire 1. Since the circular ring 21 is kept movable parallel to the bath surface, the stripper nozzle '10 is also movable parallel to the bath surface. This mobility of the stripper nozzle 10 prevents to a great extent, tearing of the wire, during the coating operation.

FIG. 5 shows a modification of the tin bath according to FIG. 4. The holder for the tube 11 is designed to be rigid. But even in this embodiment, the tube ll may be maintained in a holder in movable relation, similarly to FIG. 4. In FIG. 5, the inlet opening 14b is defined by a tube 29 which may be produced of stainless steel. This tube 29 is placed at the lower front face of the stripper nozzle, concentric to bore 14 of the stripper nozzle 10. It was found that this tube 29 helps considerably to improve the uniformity of the tin layer of the copper wire 1. It was found advantageous to select an inside diameter for the tube 29 which is at a maximum 15 mm larger than the wire diameter for the tube 29 which is at a maximum 15 mm larger than the wirediameter. Also, the tube should be as most 100 mm long.

German Disclosure Document l,52l,487, corresponds to United States Application Ser. No. 605,743 and now abandoned.

We claim:

1. Apparatus for producing tin layers or tin alloy layers on wires comprising copper or copper alloys by means of hot tin plating, with a uniform thickness of 3 ,u. across the wire circumference, comprising a tin bath or a tin alloy bath having a bath surface, a flat profiled stripper nozzle beneath said bath surface, said stripper nozzle having a bore diameter defined by a wave train, which runs between two concentric circles, the radii of said circles being adjusted to the radius of the wire to be processed therethrough, and 3 to 15 half waves being provided for every millimeter of circumference of the inner of said concentric circles.

2. The apparatus of claim 1, wherein five to eight half waves are provided for each millimeter of the circumference of the inner of said concentric circles.

3. The apparatus of claim 1, wherein the radius of the inner concentric circle is l to 10 ;1. larger than the outer tolerance limit of the radius of the wire.

4. The apparatus of claim 3, wherein the radius of the inner concentric circle is 2.5 to 5 p. larger than the outer tolerance limit of the radius of the wire.

5. The apparatus of claim 1, wherein the difference between the radii of the two concentric circles is from 20 to p" 6. The apparatus of claim 5, wherein the difference between the radii of the two concentric circles is from 40 to 60 ;l.. 

1. Apparatus for producing tin layers or tin alloy layers on wires comprising copper or copper alloys by means of hot tin plating, with a uniform thickness of >3 Mu across the wire circumference, comprising a tin bath or a tin alloy bath having a bath surface, a flat profiled stripper nozzle beneath said bath surface, said stripper nozzle having a bore diameter defined by a wave train, which runs between two concentric circles, the radii of said circles being adjusted to the radius of the wire to be processed therethrough, and 3 to 15 half waves being provided for every millimeter of circumference of the inner of said concentric circles.
 2. The apparatus of claim 1, wherein five to eight half waves are provided for each millimeter of the circumference of the inner of said concentric circles.
 3. The apparatus of claim 1, wherein the radius of the inner concentric circle is 1 to 10 Mu larger than the outer tolerance limit of the radius of the wire.
 4. The apparatus of claim 3, wherein the radius of the inner concentric circle is 2.5 to 5 Mu larger than the outer tolerance limit of the radius of the wire.
 5. The apparatus of claim 1, wherein the difference between the radii of the two concentric circles is from 20 to 80 Mu .
 6. The apparatus of claim 5, wherein the difference between the radii of the two concentric circles is from 40 to 60 Mu . 